As is well known, it is conventional to utilize a fluid or oil squeeze film damper to dampen the radial loads transmitted from the working parts of the engine through the radial bearings. Such dampers for example are disclosed in U.S. Pat. Nos. 4,213,661 granted to R. P. Marmol on July 22, 1980, 4,046,430 granted to D. F. Buono et al on Sept. 6, 1977, and 4,669,893 granted to D. Chalaire et al on June 2, 1987, all of which are assigned to UTC the assignee of this patent application.
The U.S. Pat. No. 4,669,893 exemplifies a fluid damper that includes an annular fluid chamber that surrounds the bearing and is disposed between the bearing outer race and a stationary support and is associated with the radial bearing supporting the compressor/turbine shaft of a gas turbine engine. The fluid damper serves to control the transversal orbital movement of a nonrotating cylinder induced by the vibratory energy created by unbalance in the rotating shaft. Obviously, the energy level or the amplitudes of the vibration is particularly high during a surge or loss of blade on the rotor.
Other damper designs include a segmented ring supported to a stationary support that includes a plurality of fluid filled chambers. These chambers are formed on the convex surface of each segment of the segmented ring and are bounded by an elongated circular seal sometimes referred to as in a race track which is continuously supplied with oil. The oil filled chambers are sandwiched between the convex surface and the outer race of the bearing and like the full annular fluid damper serve to dampen the vibratory motion of the shaft. In some instances a spring operatively connected to the stationary support serves to resiliently support and load the bearing. Rod springs, sometimes referred to as squirrel cages, are customarily used in these applications.
While it is conventional to dampen radial bearings with fluid dampers as described above, thrust bearings require different considerations over radial bearing inasmuch as the severe thrust loadings create significant friction to impede the operation of the fluid damper during normal rotor unbalance. An example of a fluid damper design is described in U.S. Pat. No. 4,084,861 granted to P. B. Greenberg et al on Apr. 18, 1978 and assigned to U.T.C., the assignee common to this patent application. This damper design includes an annular fluid chamber and a squirrel cage spring arrangement.
We have found that we can obviate the problems associated with the squirrel cage and the damper with the annular fluid chamber for use with thrust bearings by employing a curved beam damper design. Contemplated within the scope of the invention is a segmented curve beam having oval or sometimes referred to as race track shaped chambers with nibs strategically located on each segment to transmit the thrust loads without incurring adverse frictional loads thus permitting damping during normal rotor unbalance or other reasonable unbalance excursions.
A nib at the forward side face of the segment centrally located transmits the thrust load from the outer race to the stationary housing where it is reacted by a pair of nibs located on the rear side face at each edge of the segments. Since the nibs, which do not deflect radially, contact the bearing support housing friction is further reduced.
A mechanical stop is provided to assure minimum radial travel of the segmented ring during an exceeding high unbalance occasioned from, say, a loss of a blade.